Robustness with regard to excessive temperatures is an important design goal for power semiconductor switches such as metal-oxide-semiconductor (MOS) field effect transistors (MOSFETs) insulated gate bipolar transistors (IGBTs). A robust design may be achieved, for example, by using specific materials and design rules when manufacturing the power semiconductor devices such that heat generated by energy dissipation is transferred away from the semiconductor device. Very high temperatures can particularly occur as a result of a short-circuit condition. The generated heat spreads throughout the semiconductor device in accordance with the heat conduction properties of the constituent materials. Various approaches exist which aim either at reducing the generation of heat within the active portions of the semiconductor switch or at improving the heat transfer out of the mentioned active portions to the outer surfaces of a semiconductor chip which may be coupled to a heat sink.
One approach to improve the robustness with regard to short circuits is to apply comparably thick metal layers (for example, copper layers) at the top and bottom surface of the semiconductor chip. The high thermal conductivity spreads the heat across the whole semiconductor chip surface and thus enables a proper cooling of the device. Thus, a thick metallization layer can be regarded as a kind of heat sink. However, a remaining problem impeding heat transfer out of the silicon is the thick interlayer oxides, which electrically isolate the metal (e.g., copper) layers from the surface of the semiconductor body. The interlayer oxides have significantly lower thermal conductivity than copper (or any other metal) and thus forms a bottle-neck in the heat conduction from the active portions of the semiconductor switch to the thermal sink.